In
chemistry,
homology refers to the appearance of homologues. A
homologue (also spelled as homolog) is a
compound belonging to a series of compounds differing from each other by a repeating unit, such as a
methylene bridge --, a
peptide residue, etc. A homolog is a special case of an
analog. Examples are
alkanes and compounds with
alkyl side chains of different length (the repeating unit being a methylene group -CH
2-).